U.S. Ser. No. 60/227,015 xe2x80x9cHigh Speed and Reliable Determination of Lumber Quality Using the Tracheid Effectxe2x80x9d, by Metcalfe and Dashner, filed the same day, the disclosure of which is incorporated herein by reference.
U.S. Ser. No. 09/931,179 xe2x80x9cHigh Speed Camera Based Sensorsxe2x80x9d, by Metcalfe and Reuser, filed the same day, the disclosure of which is incorporated herein by reference.
The invention relates to TV Camera based and other electro-optical sensors and systems, providing affordable methods and apparatus for high speed scanning of dimensions and other features of objects.
The invention uses one or more light sources combined with TV cameras whose output is used as input to a computer, such as a PC. This data is analyzed to typically provide data concerning the location or dimension of objects or parts of objects and/or the presence or characteristics of certain features of objects.
The invention is particularly useful for applications relating to wood products, including boards moving at high speed on conveyor lines in sawmills. More specifically it is concerned with triangulation sensors for object dimension, shape, thickness and position determination, especially at multiple locations on moving boards up to 28 feet long and at 3 boards per second. Data taken with such sensors is used to control sophisticated sawing operations aimed at maximizing yield from boards of variant shape, particularly in their edge regions.
A large number of data points per piece (e.g. every 0.1 inch or greater) is today considered essential to obtain a high quality 3D representation of the object shape so as to optimally control sawing operations used to maximize the yield of logs sawn. The invention discloses novel methods and apparatus to achieve this goal.
Laser triangulation sensors have found favor in industry, particularly the lumber industry where, for example, requirements exist to determine shape, thickness or local contour of 28 foot long boards moving sideways on chain conveyors at 3 boards per second, in order to control the saws used to trim the boards of non conforming stock. Current trends call for more and more board sections to be taken, in order to better categorize the product and its subsequent sawing or other processing steps.
Over the last few years, sectional data density requirements have steadily progressed from one section every 6 inches of axial board length, to the existing state of the art of every one inch. This application seeks to improve this ability to every 0.1 inch or better down the length of a 16 foot board, say, while still maintaining the high quality of data with minimum latency needed to control actual process operations.
In the specific area of interest of this application in the field of wood measurement, examples of laser triangulation based sensor units specifically designed for this are Leong et al: U.S. Pat. No. 4,937,445, entitled Apparatus for determining the distances of points on a surface from a reference axis and Cielo et al, U.S. Pat. No. 5,056,922 entitled Method and apparatus for monitoring the surface profile of a moving workpiece. Both of these applications illustrate systems which represent the norm today for measuring moving boards, in which the direction of board motion is transverse to the longitudinal or long axis of the board. The lens axis, detector array and the longitudinal axis of the board are all basically in a common plane.
For the case of boards traveling in the direction of their longitudinal axis, a light stripe type system such as Chasson, U.S. Pat. No. 4,188,544 entitled Method and Apparatus for Automatically Processing a workpiece employing calibrated scanning, can be employed. Handling boards however, in this manner at high speed needed to cover all the board is very difficult.
A generic reference on dimensional and positional measurement of objects by Electro-optical means is Pryor et al: U.S. Pat No. 5,734,172 entitled Method and apparatus for electro optically determining the dimension, location and attitude of objects (the disclosure of which is incorporated by reference). Other references disclosing triangulation measurements with photo-detector arrays are; U.S. Pat. No. 4,891,772 Case et al. entitled Point and line range sensors; and Liptay-Wagner et al, U.S. Pat. No. 4,394,683 entitled New photodetector array based optical measurement systems. The use of first moment calculations to determine a image location is described in U.S. Pat. No. 4,219,847 by Pinkney et al. entitled Method and apparatus of determining the center of area or centroid of a geometrical area of an unspecified shape lying in a larger x-y scan field.
Further incorporated herein by reference is a provisional patent application entitled xe2x80x9cHigh Speed Camera based Sensorsxe2x80x9d, filed by our colleagues Leonard Metcalfe and Cash Reuser on the same day as this application.
Also incorporated by reference is an application by our co-worker, Richard McBain, entitled High speed laser Triangulation Measurements of Shape and Thickness, claiming benefit of U.S. Provisional application No. 60/135,680.
U.S. Pat. No. 5,717,199 by Carbone et al. discloses methods and apparatus by which data can be read randomly from pixels of a camera, while U.S. Pat. No. 5,982,393 by Forchheimer et al. describes methods by which computing can be done directly on pixel data using processors located on the same image chip. However, neither reference discloses methods by which such devices can actually be used to make practical measurements required in industry in an apparatus such as disclosed herein.
Categorization of lumber defects such as knots, is discussed in our copending application referenced above as well as U.S. Patents such as Mathews et al. U.S. Pat. No. 3,976,384 and Soest, U.S. Pat. No 5,703,960.
This invention relates to a significant advance over the state of the art as disclosed in Leong, Cielo et al. etc, and others for measuring boards moving transversely at the high speeds needed to provide information to real time sawing and other operations in lumber mills. One aspect covers a novel sensor arrangement, in which the camera system is oriented 90 degrees to that known heretofore, and uses novel signal processing methods to achieve the necessary data density, speed and obscuration elimination desired.
A preferred embodiment utilizes laser triangulation with a multiplicity of points, or one or more lines, said points or lines extending in the direction of the longitudinal axis of the object and perpendicular to the transfer direction of the object. Images of points on the surface of the object are determined in their position by two cameras one on each side of point or line projection direction, which as disclosed can eliminate problems with obscuration which otherwise would render inadequate a device such as that of Chasson if employed in this way.
The invention in some embodiments also utilizes a knowledge of the part itself to control the sensing characteristics to facilitate determination of object location or dimension in the presence of undesirable conditions caused by the surface condition of the object, which may be, for example, different surfaces of a moving board, or log, which face in the direction of motion or away from same.
It is noted that in the following discussion, the word xe2x80x9claserxe2x80x9d is meant to connote not only the laser device itself of whatever kind (typically a semi-conducting diode laser), but also any associated optics and power sources needed to assure that reliable optical energy can be delivered to a zone on the surface of the object to be measured. Typically, but not necessarily, such a zone is produced by focusing the radiation emanating from the laser to a small zone at the mean point of object location in the laser projection direction. In other cases cylindrical optics are used to create line projections. Optics may be either refractive, reflective or diffractive/holographic in nature.
While the preferred detector array employed for board measurement to date has been a CCD, or charge coupled device, type array (for example a Reticon 1024C linear CCD type), this application is particularly concerned with use of specialized matrix array types, including, but not limited to CMOS as well as CCD types, capable of random or quasi-random scanning of their respective pixel outputs.
It is a goal of the invention to provide a triangulation device, employing at least one photo-detector array camera and projecting on an object multiple projected laser or other light zones, which overcomes reflection, obscuration and other problems caused by object surface shape and other discontinuities while operating at the highest possible operational speed, with acceptable accuracy and at reasonable cost.
It is a further goal of the invention to provide high density data via a novel sensory arrangement in which two camera devices are disposed in the direction transverse to the object longitudinal axis for viewing light zones projected along the object longitudinal axis and for discerning from comparison of data obtained from the cameras the range data corresponding to each zone, even in the presence of object occlusions, obscurations, or areas of unusual reflectance.
It is a goal of the invention to provide means to economically and accurately measure object length as well as obtain thickness and profile related information.
It is another goal of the invention to allow the reconstruction of object curved edges and other regions measured at high speed by using interpolated or extrapolated data, for example to fill in readings obtained.
It is also a goal of the invention to provide a method for increasing the reliability of detection of projected zones on objects with variant reflectance characteristics at different portions of their surface.
It is another goal of the invention to provide a method to control sensing characteristics with respect to moving objects using a knowledge of their movement and shape.
It is a still further goal of the invention to provide a triangulation device, employing a pair of twin PSD (position sensing diode) array based cameras in a novel arrangement in the direction of object motion utilizing a projection on an object of multiple projected laser or other light zones.